Re: [PATCH 09/11] UAPI: ndctl: Fix g++-unsupported initialisation in headers [ver #2]

[Dan Williams]

On Thu, Sep 6, 2018 at 2:19 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> The following code in the linux/ndctl header file:
>
>         static inline const char *nvdimm_bus_cmd_name(unsigned cmd)
>         {
>                 static const char * const names[] = {
>                         [ND_CMD_ARS_CAP] = "ars_cap",
>                         [ND_CMD_ARS_START] = "ars_start",
>                         [ND_CMD_ARS_STATUS] = "ars_status",
>                         [ND_CMD_CLEAR_ERROR] = "clear_error",
>                         [ND_CMD_CALL] = "cmd_call",
>                 };
>
>                 if (cmd < ARRAY_SIZE(names) && names[cmd])
>                         return names[cmd];
>                 return "unknown";
>         }
>
> is broken in a number of ways:
>
>  (1) ARRAY_SIZE() is not generally defined.
>
>  (2) g++ does not support "non-trivial" array initialisers fully yet.
>
>  (3) Every file that calls this function will acquire a copy of names[].
>
> The same goes for nvdimm_cmd_name().
>
> Fix all three by converting to a switch statement where each case returns a
> string.  That way if cmd is a constant, the compiler can trivially reduce it
> and, if not, the compiler can use a shared lookup table if it thinks that is
> more efficient.
>
> A better way would be to remove these functions and their arrays from the
> header entirely.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Dan Williams <dan.j.williams@xxxxxxxxx>

Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>

...again let me know if you'll take this with g++ series or want me to
carry it directly.